1. Biological mediation of invasive plant impacts in ecosystems Duane A. Peltzer Landcare Research Lincoln, New Zealand

3. 1.NZ weeds and ecosystem processes 2.What are weed impacts? 3.Field removal experiments What is covered in this talk?

4. NZ Background > half of NZ’s flora is naturalised non- native plants; many are weeds Weeds are widely thought to reduce biodiversity and alter ecosystem processes >340 weed species are currently managed

6. IMPACT = DISTRIBUTION x ABUNDANCE x EFFECT Predicting weed impact

7. Least well understood, include: Gene-flow Biogeochemical changes (C, N, P) Disturbance regime Ecosystem engineers Interaction modification Weed effects

8. Understanding what controls the ecosystem-level impacts of exotic species as a basis for management Invasion Ecology

10. After Cote et al. 2005 ARES Modest effects Reversible threshold effects Non-reversible threshold (different stable states)

11. Kowhai River, Kaikoura, NZ

13. Dominant exotic Buddleja davidiiCoriaria arborea Dominant native ~97% of total plant biomass

14. ~15 species <0.1% of biomass ~25 species ~3% of biomass Other exotics Other natives

19. Peltzer et al. 2009 Oikos 118: 1001

26. Dickie et al. 2010 New Phytologist

27. Nematode community shifts Dehlin et al. 2008

30. Preferred Not selected Avoided Forsyth et al. 2002, Richardson et al. unpublished

31. Kurokawa, Peltzer, Wardle 2010 Functional Ecology

34. PossumsRats Vegetation /fruit Inverts? Birds Control

35. Key points Small species matter! Weeds have biological legacies + change ecosystem processes (effects) Containment or early control is best

39. Peltzer et al. 2010 GCB 16:732.